As a countermeasure against global warming, it is Japan's duty to reduce, between 2008 and 2012, the emission volume of greenhouse gas by an average of 6% per annum from the level of 1990. However, in 2002, the volume of Japan's greenhouse-gas emissions increased by 7.6% over the volume for 1990. If this continues, it will be difficult to achieve the 6% reduction goal. Therefore, the government has adopted the Kyoto Protocol Target Achievement Plan, which has standards stricter than those of existing countermeasures against global warming, and which presents goals for reducing the CO2 that is emitted when energy is utilized in various sectors of societal activity. The plan provides that, for 2010 the volume of CO2 emissions from the energy-conversion sector (e.g., power plants) should be 16.1% less than in 1990, the volume from the industrial sector should be 8.6% less, the volume from the transportation sector should not be more than 15.1% higher, the volume from the other sector including the service sector should not be more than 15.0% higher, and the volume of household emissions should not be more than 6.0% higher. However, in Japan, energy-saving measures have already been implemented in the industrial sector, where the largest reduction in CO2 emission volume can be expected. Therefore, the cost of further reducing carbon dioxide emissions will be significantly high, which is a problem.
Greenhouse gas includes six kinds of gases, e.g., carbon dioxide, methane, and hydrochlorofluorocarbon. In Japan, however, 90% or more of the greenhouse gas that is emitted is carbon dioxide. The United States and the European Union are storing carbon dioxide underground as an effective measure for reducing that greenhouse gas, but in Japan, storing carbon dioxide underground is considered unsuitable due to Japan's geological conditions as well as the frequent earthquakes that occur in this country. The conventional method of storing carbon dioxide underground is to seal carbon dioxide, which is in the form of a supercritical fluid (i.e., under high temperature and high pressure, where a distinction between liquid and gas cannot be made), under a rigid sealing layer or caprock layer. However, in Japan it is difficult to find a place that is economical and suitable for that type of storage. Patent Document 1, “Method for Operating a System of Separation and Recovery of Carbon Dioxide By Using a Steel Plant Facility,” discloses a system for separating and recovering carbon dioxide from byproduct gases emitted from a steel plant. The carbon dioxide that is separated and recovered from the steel plant is fed to an immobilizing facility via a transportation means such as a pipe. The carbon dioxide in the immobilizing facility is then injected into an aquifer underground, injected into a depleted gas field, or stored in the ocean, so that the carbon dioxide is immobilized. Patent Document 2, “Device for Liquefaction and Sedimentation of Gases,” discloses that seawater and carbon dioxide that has been liquefied under high pressure are alternately pumped and fed deep into the sea.    Patent Document 1: Japanese Patent Application Publication No. 2004-237167    Patent Document 2: Japanese Patent Application Publication No. 2000-227085